Fiber optics are widely used as a medium for transmitting voice and data signals. As a transmission medium, light provides advantages over traditional electrical communication techniques. For example, light signals allow for relatively high transmission rates as well as for transmission over great distances without signal loss, and light signals are resistant to electromagnetic interferences that can interfere with electrical signals.
Optical communications systems present a number of implementation challenges. For example, the data carried by light signal must be converted from an electrical signal to light at the sending device, and then converted from light back to an electrical signal at the receiving device. Thus, in an optical communication system, it is typically necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and to, in turn, couple the device to an electronic system such as a switching system or processing system.
These connections can be facilitated by modularizing the transceiver device used at both the sending and receiving device. Various transceiver module configurations are known for interfacing with a host device, such as a host computer, switching hub, network router, switch box, computer I/O and the like. For such implementations, it is standard for transceivers to be inserted into cages, such as, for example a stacked cage 10 shown in FIG. 1A. The cage 10 is a structure for receiving transceivers and comprises sides 12, top 16 and bottom 18 (not seen in view illustrated in FIG. 1). Additionally, the cage 10 includes a plurality of bays 14a, 14a′, 14b, 14b′. The cage illustrated in FIG. 1A is a stacked cage, meaning that one set of bays 14a, 14a′ is stacked on top of another set of bays 14b, 14b′. 
The internal dimensions of the bays 14a, 14a′ 14b, 14b′ are typically standardized to the type of transceiver the cage 10 is meant to house, including for example, Small Form-Factor (SFF) or SFF-Pluggable (SFP) format. Additionally, more than one cage 10 can be used in a hub or network switch 20, as illustrated in FIG. 1B. FIG. 1B, illustrates a portion of a network switch 20, with a housing comprised of top 22, front face 24, sides 26, and bottom (not illustrated in FIG. 1B). The network switch 20 includes one or more cages 10, illustrated in FIG. 1B as one cage 10, with transceiver modules 16a, 16a′ inserted into the upper bays 14a, 14a′, and transceiver modules 16b, 16b′ inserted into lower bays 14b, 14b′. 
It is desirable to fit as many transceivers 16a, 16a′, 16b, 16b′ as possible into each cage 10, keeping in mind the need for each bay 14a, 14a′, 14b, 14b′ to be sized according to the standards for the applicable type of transceiver. Similarly, it is desirable to put as many cages 10 as possible into standard sized network switches 20. However, packing transceivers together so densely, especially as the transceiver size decreases and transceivers are stacked vertically as illustrated in FIGS. 1A and 1B, creates heat which can be detrimental to the performance of the transceivers. For instance, when the transceivers are optical transceivers, the optical elements and electrical components of the transceiver, such as light sources (e.g., lasers), light sensors, lenses and other optics, digital signal driver and receiver circuits, etc. of each transceiver must be kept below certain temperatures to ensure proper operation.
As the protocols used in optical networks increase in transmission speed, the heat generated by the transceivers typically increases, especially for smaller transceiver modules. For instance, 10-Gigabit transceivers generally require heat dissipation mechanisms. The heat emitted by the electronics and opto-electronics in transceivers 16a, 16a′, 16b, 16b′ such as that shown in FIG. 1B is commonly conducted away from transceivers by metallic portions of the cage 10 into which the transceivers are plugged. As illustrated in FIG. 2, cage 10 connectively coupled to a PCB board 30 may be inserted into a network switch 20 for use in an optical system. The network switch 20 can include apertures or openings in the rear 28 of the housing (or the housing of the network switch 20 may not have a rear cover) allowing air flow 32 to the back of and over the top surface 16 of the cage 10 in order to cool the cage 10 and dissipate the heat generated by the transceivers plugged into the cage 10 (not shown).
However, such systems are inefficient and do not equally cool the upper and lower transceivers in a stacked-cage 10. Such unequal cooling makes it difficult to properly regulate the temperature of all of the transceivers equally, and to know with any confidence that the transceivers inserted into the lower bays 14b, 14b′ are being properly cooled to ensure efficient operation.